Projection lens apparatus and projection type image display apparatus

ABSTRACT

A projection type image display apparatus having an image display element outputting an image ray, a projection lens apparatus for performing overhead projection of the image ray from the image display element, the projection lens apparatus having a plurality of lens elements, a reflection mirror reflecting the image ray from the projection lens apparatus, and a screen on which the image ray reflected by the reflection mirror is projected. An optical axis of the projection lens apparatus is decentered from a center of the screen.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/903,510, filedJul. 13, 2001, now U.S. Pat. No. 6,560,041 the subject matter of whichis incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection lens apparatus forallowing a source light to be made incident in an image displayapparatus so that an overhead projection of the reflected light or thetransmitted light is performed on a projection screen, and also relatesto a projection type image display apparatus equipped with theprojection lens apparatus.

2. Description of the Prior Art

The main stream of a projection type image display apparatus has been atype that performs an overhead projection of an image formed in a CRT.In order to improve the efficiency of light usage, and reduce the sizeand the weight of the apparatus, a projection type image displayequipped with a liquid crystal display element and a micro mirrordisplay element (hereinafter, referred to as a DMD element) instead of aCRT has been recently developed. This projection type image displayapparatus is configured such that a source light is modulated bytransmitting or reflecting it at each pixel in accordance with videosignals applied to the above display element, thereby allowing aprojection lens apparatus to perform a overhead projection and thus forman image.

Although the image display apparatus equipped with a CRT is capable ofelectrically compensating distortion aberration of a projection image,the image display apparatus equipped with a liquid crystal displayelement or a DMD element is not. For that reason, the latter apparatusis required to optically compensate the distortion aberration.

A projection type lens apparatus using liquid display elements also hasbeen developed as set forth, e.g., in JP-A-11-149041 specification,however, it has a drawback of a short back focus of about 20 mm.

SUMMARY OF THE INVENTION

In view of the above problems, it is an object of the present inventionto provide a projection lens apparatus for forming an image with highresolution by satisfactorily compensating various kinds of aberration,while securing an appropriate back focus so that another opticalcomponent is arranged between the projection lens apparatus and an imagedisplay element such as a liquid crystal display element and a DMDelement.

In order to attain the above described object, a projection lensapparatus according to the present invention is designed to satisfy thefollowing conditions (1) to (4), in which a first lens group having anegative refracting power, a second lens group having a positiverefracting power, and a third lens group having a positive refractingpower are arranged from a projection screen side (a light emission side)to an image display element side (a light incidence side) in this order.1.4<|f ₁ |/f  (1)2.8<f ₃ /f  (2)3.6<f _(b) /f  (3) 0.1<|f ₁ /f ₂₃|<0.3  (4)here, f, f₁, and f₃ represent focal lengths of a whole lens system, afirst lens group, and a third lens group, respectively, and f₂₃represents a combined focal length of a second and third lens groups,and further f_(b) represents a back focus of the whole lens system.

Power distribution of the first to third lens groups as defined aboveallows the projection lens apparatus to compensate satisfactorilyvarious kinds of aberration, while the compactness and the wide-angle ofthe apparatus are achieved.

The conditions (1) and (2) are set to reduce chromatic aberration ofmagnification by controlling powers of the first and third lens groupswhich are to have a maximum off-axis ray height. It becomes difficult tocompensate the chromatic aberration of magnification, when |f₁|/f andf₃/f become equal to or fall below the respectively corresponding lowerlimits.

The condition (3) is set to secure an appropriate back focus. Whenf_(b)/f becomes equal to or falls below its lower limit, the back focusbecomes smaller, accordingly making it difficult to arrange an opticalcomponent between the lens apparatus and the liquid crystal imagedisplay such as the liquid crystal display element and the DMD element.

The condition (4) is set to secure an appropriate back focus and toreduce distortion aberration. When |f₁/f₂₃| becomes equal to or exceedsits upper limit, positive powers of the second and third lens groupsincrease, accordingly making it difficult to secure an appropriate backfocus. On the other hand, a negative power of the first lens groupincreases, thereby causing negative distortion aberration to increase,when |f₁/f₂₃| becomes equal to or falls below its lower limit.

The projection lens apparatus according to the present invention alsomay allow the first, second and third lens groups to have a sphericalsurfaces. If every lens group has an aspherical surface thereat, thefirst and third lens groups compensate aberration such as distortionaberration and chromatic aberration of magnification on the asphericalsurfaces thereof, and the second lens group compensates aberration of anon-axis ray on its aspherical surface. This configuration permits thelens apparatus to have more versatility of possible compensation ofaberration, accordingly to perform further compensation of aberration.

In particular, using an aspherical surface as an emission surface of athird lens of the third lens group, having a large off-axis ray height,serves to effectively compensate aberration of an off-axis ray. Using anaspherical surface also as an incidence surface of a second lens of thesecond lens group serves to most effectively compensate aberration of anon-axis ray.

Using a plastic lens as a first lens of the first lens group, having alargest diameter among lenses of the projection lens apparatus accordingto the present invention, allows the apparatus according to the presentinvention to reduce its weight. However, since the plastic lens changesin shape according to changes in temperature and humidity, the lenscharacteristics thereof such as lens focus and MTF deteriorates, whenthe plastic lens has a large power. The condition below is intended tocontrol the power of the plastic lens so that the lens characteristicsdo not deteriorate even when the plastic lens changes in shape accordingto changes in temperature and humidity.7<|f _(L1) /f|  (5)

A typical plastic lens has poor accuracy in shape and large deviationsin shape accuracy compared to a glass lens. To suppress thedeterioration of the plastic lens having deviations in shape accuracy, aray is made incident on the plastic lens, in a direction substantiallyperpendicular to the plastic lens, serving as the first lens of thefirst lens group in the projection lens apparatus according to thepresent invention. This configuration allows the plastic lens to have alarger tolerance in shape and enhance its manufacturability.

Achieving the compactness and the wide-angle of the projection lensapparatus is required to reduce the size of the project type imagedisplay apparatus. Decentering the optical axis of the lens apparatusagainst the center of the projection screen allows the projection typeimage display apparatus to be downsized further. Decentering theprojection lens apparatus against the center of the projection screenrequires decentering a Fresnel screen against the projection screen.

When the optical axis of the projection lens apparatus is decenteredagainst the center of the projection screen, ratios of peripheral lightquantities at the upper and lower parts of the screen are generallydifferent because of different distances from the optical axis of theprojection lens apparatus to the upper and lower parts of the screen. Inthe projection type image display apparatus according to the presentinvention, difference in ratios of peripheral light quantities at theupper and lower parts of the screen is designed to be 10% or less sothat brightness at the upper and lower parts of the screen issubstantially equal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a projection lens apparatus according to afirst embodiment of the present invention;

FIG. 2 is an illustration of spherical aberration of the projection lensapparatus according to the first embodiment;

FIG. 3 is an illustration of astigmatism of the projection lensapparatus according to the first embodiment;

FIG. 4 is an illustration of distortion aberration of the projectionlens apparatus according to the first embodiment;

FIG. 5 is a schematic view of a projection lens apparatus according to asecond embodiment of the present invention;

FIG. 6 is an illustration of spherical aberration of the projection lensapparatus according to the second embodiment;

FIG. 7 is an illustration of astigmatism of the projection lensapparatus according to the second embodiment;

FIG. 8 is an illustration of distortion aberration of the projectionlens apparatus according to the second embodiment;

FIG. 9 is a schematic view of a projection lens apparatus according to athird embodiment of the present invention;

FIG. 10 is an illustration of spherical aberration of the projectionlens apparatus according to the third embodiment;

FIG. 11 is an illustration of astigmatism of the projection lensapparatus according to the third embodiment;

FIG. 12 is an illustration of distortion aberration of the projectionlens apparatus according to the third embodiment;

FIG. 13 is a schematic view of a projection lens apparatus according toa fourth embodiment of the present invention;

FIG. 14 is an illustration of spherical aberration of the projectionlens apparatus according to the fourth embodiment;

FIG. 15 is an illustration of astigmatism of the projection lensapparatus according to the fourth embodiment;

FIG. 16 is an illustration of distortion aberration of the projectionlens apparatus according to the fourth embodiment;

FIG. 17 is a schematic view of a projection lens apparatus according toa fifth embodiment of the present invention;

FIG. 18 is an illustration of spherical aberration of the projectionlens apparatus according to the fifth embodiment;

FIG. 19 is an illustration of astigmatism of the projection lensapparatus according to the fifth embodiment;

FIG. 20 is an illustration of distortion aberration of the projectionlens apparatus according to the fifth embodiment;

FIG. 21 is a schematic view of a projection type image display apparatusin which there is incorporated the projection lens apparatus accordingto any one of the above embodiments; and

FIG. 22 is an illustration of a vignetting factor of the projection lensapparatus according to any one of the above embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the attached drawings, preferred embodiments of thepresent invention will be described. FIGS. 1, 5, 9, 13, and 17 areillustrations of projection lens apparatuses according to theembodiments of the present invention. The following description will befocused mainly on FIG. 1, and descriptions on FIGS. 5, 9, 13, and 17will be omitted since these figures are considered to be understood fromdata in Tables 2 to 5 and on the analogy of the description on FIG. 1.

FIG. 1 is a schematic view of a first embodiment of the projection lensapparatus and its associated optical components showing, from aprojection screen (not shown) or the left side of the plane of thefigure, a first lens group 1, a second lens group 2, a third lens group3, a total reflection prism (hereinafter, referred to as a TIR prism) 5,and a DMD element 6 in this order. The above three lens groups 1 to 3constitute a projection lens apparatus 4. A ray emitted from a lightsource is made incident on an incidence plane 51 of the TIR prism 5, andis totally reflected at a total reflection plane 52 of the TIR prism 5,and then is made incident on the DMD element 6. After reflected on anactive plane of the DMD element 6, the incident ray transmits the TIRprism 5, and is made incident on the projection lens apparatus 4, andthen is projected on the screen.

The projection lens apparatus 4 is provided with the first lens group 1having a negative refracting power, the second lens groups 2 having apositive refracting power, and third lens groups 3 having a positiverefracting power. The first lens group 1 includes a first lens 11 aswell as a second lens 12 of negative meniscus lenses facing their convexsurfaces toward the screen, and a third lens 13 of a biconcave lens, inaddition to a fourth lens 14 of a biconvex lens. The second lens group 2includes a fifth lens 21 of a biconvex lens, an aperture 22, and a sixthlens 23 of a biconvex lens. The third lens group 3 includes a seventhlens 31 and an eighth lens 32 having a mating face therebetween, a ninthlens 33 facing its concave surface toward the screen, and a tenth lens34 of a biconvex lens.

In the first embodiment shown in FIG. 1, a resin is bonded on onesurface of each of the sixth lens 23 of the second lens group 2 and theninth lens 33 of the third lens group 3 (hereinafter, these lenses arereferred to as hybrid lenses). While the resin-bonded surface of each ofthe hybrid lenses is spherical, the opposite surface thereof isaspherical. The first lens 11 of the first lens group 1 is made fromplastic and the largest in diameter among the lenses in the projectionlens apparatus 4. Using a plastic lens as the first lens 11 serves toreduce the weight of the projection lens apparatus 4. The plastic lens,however, has a problem such that the lens changes in shape according tochanges in temperature and humidity, thereby causing deterioration ofits lens characteristics. Controlling a power of the plastic lens isrequired to suppress the deterioration of the lens characteristics dueto temperature and humidity. To minimize the deterioration of the lenscharacteristics, the present invention sets the following condition:7<|f _(L1) /f|

-   here, f: a focal length of the whole lens system; and    -   F_(L1): a focal length of the first lens 11 of the first lens        group 1.        The plastic lens has generally poor accuracy in shape compared        to a glass lens. To suppress the deterioration of the lens with        poor accuracy in shape, a ray is made incident on the first lens        11 in a direction substantially perpendicular to the first lens        11 of the first lens group 1 in the projection lens apparatus 4        according to the present invention. This configuration allows        the plastic lens to have a larger tolerance in shape and enhance        its manufacturability. The plastic lens has aspherical surfaces,        thereby serving to compensate distortion aberration.

The ninth lens 33 of the third lens group 3 is a hybrid lens having anaspherical surface. This serves to compensate off-axis aberrationeffectively because of a large off-axis ray height of the hybrid lens.The sixth lens 23 of the second lens group 2 arranged close to theaperture 22 is also a hybrid lens having an aspherical surface, therebyserving to compensate on-axis aberration effectively. With thisconfiguration, a desired back focus is secured so that the TIR prism 5is arranged between the projection lens apparatus 4 and the DMD element6. Consequently, the projection lens apparatus 4 is allowed tocompensate various kinds of aberration satisfactorily and realizeperforming a high-resolution projection, while achieving itsminiaturization and wide-angle. In order to realize these states, it isrequired to meet the following conditions:1.4<|f ₁ |/f  (1)2.8<f ₃ /f  (2)3.6<f _(b) /f  (3)0.1<|f ₁ /f ₂₃|0.3  (4)

-   here, f: a focal length of the whole lens system;    -   f_(b): a back focus of the whole lens system;    -   f₁: a focal length of the first lens group;    -   f₃: a focal length of the third lens group; and    -   f₂₃: a combined focal length of the second and third lens        groups.        The conditions (1) and (2) are set to reduce chromatic        aberration of magnification by controlling the powers of the        first and third lens groups having a maximum off-ray height. It        becomes difficult to compensate the chromatic aberration of        magnification, when |f₁|/f and f₃/f become equal to or fall        below the respectively corresponding lower limits.

The condition (3) is set to secure an appropriate back focus. The backfocus becomes shorter, when f_(b)/f becomes equal to or falls below itslower limit. In this case, there is insufficient space left between theprojection lens apparatus and a liquid crystal display element or theDMD element in which an optical element is arranged.

The condition (4) is set to secure the appropriate back focus and reducenegative distortion aberration. When |f₁/f₂₃| becomes equal to orexceeds its upper limit, the positive powers of the second and thirdlens groups become larger, thereby leading to difficulty in securing theappropriate back focus. When |f₁/f₂₃| becomes equal to or falls belowits lower limit, the negative power of the first lens group becomeslarger, thereby leading to increase in negative distortion aberration.

Referring now to the attached tables, the embodiments of the presentinvention will be described in further detail. Table 1 corresponds toFIG. 1, which is a schematic view of the projection lens apparatusaccording to the first embodiment of the present invention. Similarly,Tables 2, 3, 4, and 5 correspond to FIGS. 5, 9, 13, and 17,respectively. In these tables, R_(i) represents a radius of curvature ofan ith surface counted from the screen including the surface of theaperture. D_(i) represents a distance, on the optical axis, from the ithto (i+1)th surfaces counted from the screen. N_(j) and ν_(j) represent arefractive index and an Abbe number (d line) of the jth lens countedfrom the screen.

When R_(i), K, h, and A, B, C, D, etc., are given, a shape of anaspherical surface is specified in the following widely used equation:

 Z=(1/R _(i))·h ²/[1+√{1−(K+1)·(1/R _(i))² ·h ² }]+A·h ⁴ +B·h ⁶ +C·h ⁸+D·h ¹⁰+ . . .

here, Z: an axis in the optical axis;

-   -   R_(i): a radius of curvature of an ith surface on the optical        axis;    -   K: a conical constant;    -   h: an axis in the radium direction of a lens; and    -   A, B, C, D, etc.: high order coefficients of the aspherical        surface.

TABLE 1 i j R_(i) D_(i) N_(i) υ_(j) 1 1 56.822 5 1.499091 58.0 2 24.18612.13 3 2 59.369 2 1.62041 60.3 4 21.691 12.58 5 3 −32.19 2 1.74400 44.96 31.969 4.46 7 4 298.82 4.99 0.84666 23.8 8 −50.963 0.52 9 5 31.1517.49 1.65412 39.6 10 −144.61 23.39 11 8 7.6 12 6 −526.002 0.1 1.52020052.0 13 7 5513.648 4.84 1.49700 81.6 14 −12.03 0.5 15 8 −12.099 21.75520 27.5 16 9 25.096 6.93 1.49700 81.6 17 −24.778 0.51 18 10 −85.75.52 1.49700 81.6 19 11 −23.628 0.1 1.520200 52.0 20 −26.797 0.5 21 12186 6.04 1.84666 23.8 22 −39.674 5 23 13 8 27 1.51680 64.2 24 8 4.5 2514 8 2.75 1.47200 55 26 8 1.55Aspherical Surface:

-   1st surface K: 2.068172, A: −9.034348e-7,    -   B: 2.140360e-9, C: −1.175769e-12,    -   D: 2.708077e-16-   2nd surface K: −1.161402, A: −4.055402e-7,    -   B: −5.42700e-10, C: 8.850174e-12,    -   D: −1.234473e-14-   12th surface K: −6729.736862, A: −4.477155e-5,    -   B: −1.779039e-7, C: 1.971636e-9,    -   D: −1.147868e-11-   20th surface K: 1.456989, A: 4.909620E-6,    -   B: 2.770520e-9, C: 2.103590e-11,    -   D: 3.609500e-14-   F-number: FNO=2.75 half field angle: ω=43.9°    -   f: 11.28, f_(b): 40.8, f₁: −17.1, f₃: 48.7, f₂₃: 81.5        |f ₁ |/f=1.52        f ₃ /f=4.3        f _(b) /f=3.62        |f ₁ /f ₂₃|=0.21        |f _(L1) /f|=7.98

Spherical aberration, astigmatism, and distortion aberration related toTable 1 are shown in FIGS. 2, 3, and 4, respectively. In these figures,G, R, and B indicate aberration of the wavelengths of rays of 555 nm,650 nm, and 450 nm, respectively. S and M indicate, respectively, asagittal image surface and a meridional image surface of a wavelength ofa ray of 555 nm. FIGS. 2 to 4 apparently indicate that the aberrationshown in the above figures are satisfactorily compensated, accordinglyrealizing lens characteristics of the projection lens apparatusnecessary for high image quality. Although a DMD element is employed asan image display element in the above-described embodiment, a liquidcrystal display element or a display element, which transmits andreflects rays for forming an image by using electrical signals, may beemployed instead of the DMD element.

TABLE 2 i j R_(i) D_(i) N_(i) υ_(j) 1 1 100 3.3 1.490901 58.0 2 27.9738.72 3 2 53.502 2 1.62041 60.3 4 24.705 11.81 5 3 411049.782 4 1.4909158.0 6 22.355 15.77 7 4 36.502 4.67 1.84666 23.8 8 −5528.298 19.79 9 86.8 10 5 −2031.293 3.01 1.48749 70.4 11 −27.791 2.765 12 6 −18.102 21.80518 25.5 13 7 36.397 5 1.48749 70.4 14 −40.088 1 15 8 352.742 4.481.48749 70.4 16 −38.889 1 17 9 71.023 7.04 1.58144 40.9 18 −39.912 1 1910 425.704 5.06 1.49091 58.0 20 −43.288 5 21 11 8 27 1.51680 64.2 22 84.5 23 12 8 2.75 1.47200 55.0 24 8 1.55Aspherical Surface:

-   1st surface K: 0, A: 1.303107Ee-3, B: 1.54150e-6,    -   C: 1.185250e-9, D: −5.127177e-13-   2nd surface K:0, A:5.820000e-4, B: 2.944327e-7,    -   C: −4.041408e-9, D: −3.178235e-13-   5th surface K: −683119333.312, A: 7.560320e-4,    -   B: −9.918486e-6, C: 4.248327e-8,    -   D: −7.666378e-11-   6th surface K: −1.907139, A: 1.750551e-3,    -   B: −2.284930e-5, C: 1.382748e-7,    -   D: −2.934505e-10-   19th surface K: 0, A: −5.439591e-4, B: −3.067743e-6,    -   C: 1.206313e-8, D: 6.496498e-12-   20th surface K: 0, A: 3.892849e-4, B: −3.091477e-6,    -   C: 1.131288e-8, D: 1.049618e-11-   F-number: FNO=2.75 half field angle: ω=43.9°    -   f: 11.23, f_(b): 40.8, f₁: −16.6, f₃: 33.3, f₂₃: 59.1        |f ₁ |/f=1.48        f ₃ /f=2.97        f _(b) /f=3.62        |f ₁ /f ₂₃|=0.288        |f _(L1) /f|=7.12

Spherical aberration, astigmatism, and distortion aberration related toTable 2 are shown in FIGS. 6, 7, and 8, respectively. In these figures,G, R, and B indicate aberration of the wavelengths of rays of 555 nm,650 nm, and 450 nm, respectively. S and M indicate, respectively, asagittal image surface and a meridional image surface of a wavelength ofa ray of 555 nm.

FIGS. 6 to 8 apparently indicate that the aberration shown in the abovefigures are satisfactorily compensated, accordingly realizing lenscharacteristics of the projection lens apparatus necessary for highimage quality.

TABLE 3 i j R_(i) D_(i) N_(i) υ_(j) 1 1 60.605 5 1.499091 58.0 2 24.9036.5 3 2 43.695 2 1.62041 60.3 4 19.327 15.35 5 3 −36.121 2 1.74400 44.96 31.698 4.52 7 4 135.746 5.1 0.84666 23.8 8 −64.108 0.5 9 5 31.252 7.971.65412 39.6 10 −194.4 26.06 11 8 7 12 6 −273.905 0.1 1.520200 52.0 13 7−280.909 4.66 1.49700 81.6 14 −12.338 0.5 15 8 −12.754 2 1.75520 27.5 169 23.486 6.87 1.49700 81.6 17 −25.81 0.5 18 10 −78.468 6.04 1.49700 81.619 11 −21.737 0.1 1.520200 52.0 20 −24.296 0.5 21 12 470.507 5.931.84666 23.8 22 −36.23 5 23 13 8 27 1.51680 64.2 24 8 4.5 25 14 8 2.751.47200 55 26 8 1.55Aspherical Surface:

-   1st surface K: 2.429735, A: 1.883753e-6,    -   B: −3.060454e-9, C: 2.691520e-12,    -   D: −1.704096e-15-   2nd surface K: −1.097959, A: −5.144892e-7,    -   B: −8.354796e-9, C: −3.030524e-12,    -   D: 8.085546e-15-   12th surface K: −6006.527896, A: −9.250468e-5,    -   B: 5.790455e-7, C: −1.088606e-8,    -   D: 6.718634e-11-   20th surface K: 1.170151, A: 5.679944E-6,    -   B: 8.160707e-9, C: 8.28354e-12,    -   D: 1.159747e-13-   F-number: FNO=2.75 half field angle: ω=43.9°    -   f: 11.25, f_(b): 40.8, f₁: −18.1, f₃: 43.68, f₂₃: 93.15        |f ₁ |/f=1.61        f ₃ /f=3.88        f _(b) /f=3.62        |f ₁ /f ₂₃|=0.19        |f _(L1) /f|=8

Spherical aberration, astigmatism, and distortion aberration based onTable 3 are shown in FIGS. 10, 11, and 12, respectively. In thesefigures, G, R, and B indicate aberration of the wavelengths of rays of555 nm, 650 nm, and 450 nm, respectively. S and M indicate,respectively, a sagittal image surface and a meridional image surface ofa wavelength of a ray of 555 nm. FIGS. 10 to 12 apparently indicate thatthe aberration shown in the above figures are satisfactorilycompensated, accordingly realizing lens characteristics of theprojection lens apparatus necessary for high image quality.

TABLE 4 i j R_(i) D_(i) N_(i) υ_(j) 1 1 55.203 5 1.499091 58.0 2 23.85667.977 3 2 51.569 2 1.62041 60.3 4 20.953 14.07 5 3 −33.488 2 1.7440044.9 6 31.698 4.65 7 4 242.91 5.5 0.84666 23.8 8 −56.232 0.52 9 5 32.2677.9 1.65412 39.6 10 −135.746 24.87 11 8 7.5 12 6 −1072.605 0.1 1.52020052.0 13 7 5513.648 4.69 1.49700 81.6 14 −12.467 0.5 15 8 −12.562 21.75520 27.5 16 9 24.265 7.07 1.49700 81.6 17 −24.809 0.5 18 10 −75.2565.66 1.49700 81.6 19 11 −22.694 0.1 1.520200 52.0 20 −25.996 0.5 21 12370.391 6.07 1.84666 23.8 22 −36.397 5 23 13 8 27 1.51680 64.2 24 8 4.525 14 8 2.75 1.47200 55 26 8 1.55Aspherical Surface:

-   1st surface K: 2.068171, A: 3.704251e-7,    -   B: −1.773038e-9, C: 2.586699e-12,    -   D: −1.350369e-15-   2nd surface K: −1.080023, A: −3.950647e-7,    -   B: −1.071853e-8, C: 1.462552e-11,    -   D: −1.035022e-14-   12th surface K: −6729.726862, A: −4.546386e-5,    -   B: −1.908974e-7, C: 2.662512e-9,    -   D: −2.171104e-11-   20th surface K: 1.349085, A: 6.028083E-6,    -   B: 5.573375e-9, C: 1.681841e-11,    -   D: 5.542812e-14-   F-number: FNO=2.75 half field angle: ω=43.9°    -   f: 11.2578, f_(b): 40.8, f₁: −17.42, f₃: 46.14, f₂₃: 90.02        |f ₁ |/f=1.55        f ₃ /f=4.10        f _(b) /f=3.62        |f ₁ /f ₂₃|=0.12        |f _(L1) /f|=7.99

Spherical aberration, astigmatism, and distortion aberration based onTable 4 are shown in FIGS. 14, 15, and 16, respectively. In thesefigures, G, R, and B indicate aberration of the wavelengths of rays of555 nm, 650 nm, and 450 nm, respectively. S and M indicate,respectively, a sagittal image surface and a meridional image surface ofa wavelength of a ray of 555 nm. FIGS. 14 to 16 apparently indicate thatthe aberration shown in the above figures are satisfactorilycompensated, accordingly realizing lens characteristics of theprojection lens apparatus necessary for high image quality.

TABLE 5 i j R_(i) D_(i) N_(i) υ_(j) 1 1 99.901 5 1.490901 58.0 2 27.8065.99 3 2 36.686 2 1.62041 60.3 4 23.142 14.769 5 3 147.145 4.2 1.4909158.0 6 15.898 17.55 7 4 37.324 4.504 1.84666 23.8 8 −338.388 16.5 9 86.022 10 5 148.210 2.88 1.48749 70.4 11 −35.173 2.733 12 6 −20.098 21.80518 25.5 13 7 23.125 5.217 1.48749 70.4 14 −38.451 1.550 15 8581.969 4.085 1.48749 70.4 16 −44.686 1 17 9 115.239 7.073 1.58144 40.918 −30.898 1 19 10 −1723.784 5.117 1.49091 58.0 20 −38.589 5 21 11 8 271.51680 64.2 22 8 4.5 23 12 8 2.75 1.47200 55.0 24 8 1.55Aspherical Surface:

-   1st surface K: −26.973907, A: 1.268671Ee-5,    -   B: −1.401240e-8, C: 9.599903e-12,    -   D: −3.473665e-15-   2nd surface K: −0.043044, A: 6.080164e-5,    -   B: 1.133503e-9, C: −3.810279e-11,    -   D: 7.928239e-17-   5th surface K: −106.491112, A: 4.681539e-6,    -   B: −1.235157e-7, C: 4.670941 e-10,    -   D: −7.569594e-13-   6th surface K: −719376, A: 4.522386e-6,    -   B: −2.621143e-7, C: 1.498970e-9,    -   D: −3.115547e-12-   19th surface K: 8181.539060, A: −1.735505e-5,    -   B: −3.594589e-8, C: 3.445454e-12,    -   D: −7.173390e-14-   20th surface K: 1.780692, A: −5.749135e-6,    -   B: −3.207989e-8, C: 3.733309e-11,    -   D: −9.642571 e-14-   F-number: FNO=2.75 half field angle: ω=43.9°    -   f: 11.257, f_(b): 40.8, f₁: −15.94, f₃: 32.6, f₂₃: 53.95        |f ₁ |/f=1.42        f ₃ /f=2.89        f _(b) /f=3.62        |f ₁ /f ₂₃|=0.295        |f _(L1) /f|=7.10

Spherical aberration, astigmatism, and distortion aberration based onTable 5 are shown in FIGS. 18, 19, and 20, respectively. In thesefigures, G, R, and B indicate aberration of the wavelengths of rays of555 nm, 650 nm, and 450 nm, respectively. S and M indicate,respectively, a sagittal image surface and a meridional image surface ofa wavelength of a ray of 555 nm. FIGS. 18 to 20 apparently indicate thatthe aberration shown in the above figures are satisfactorilycompensated, accordingly realizing lens characteristics of theprojection lens apparatus necessary for high image quality.

FIG. 21 is a schematic view of a projection type image display apparatusequipped with the projection lens apparatus according to any of theembodiments of the present invention. A light emitted from a lightsource is made incident on the DMD element 6, and then a light reflectedthereat is made incident on the projection lens apparatus 4. Theincident light is emitted at the projection lens apparatus 4, andreflected at a mirror 7. Thus, an overhead projection of an image formedat the DMD element 6 is performed on the projection screen 8. The mirror7 is intended to bend the light path of the light emitted at theprojection lens apparatus 4 so as to reduce the size of the projectiontype image display apparatus 9. Additionally, the miniaturization andwide-angle of the projection lens apparatus 4 serves to reduce the sizeof the projection type image display apparatus 9.

Decentering the optical axis of the projection lens apparatus 4 againstthe center of the screen 8 allows each component in the projection typeimage display apparatus 9 to be arranged in an optimal manner, therebyachieving further miniaturization of the projection type image displayapparatus 9. In addition, this decentration accompanies making thecenter of a Fresnel screen to be decentered.

FIG. 22 shows vignetting factor vs. distance from the center of theprojection screen. FIG. 22 indicates that, since the projection lensapparatus 4 has a high vignetting factor, the projection lens apparatus4 used for the projection type image display apparatus 9 serves to forma bright image, favorably comparable with the one on the center of thescreen, even on the periphery of the screen. Decentering the opticalaxis of the projection lens apparatus 4 against the center of the screen8 as described above generally causes the projection lens apparatus 4 tohave a vignetting factor different from the one, respectively, at theupper and lower parts of the screen, because of different object heightsfrom the optical axis of the projection lens apparatus 4. This leads todifferent ratios of peripheral light quantities at the upper and lowerparts of the screen, consequently ending up luminance unevenness on thescreen. On the other hand, the projection lens apparatus according toany of the embodiments of the present invention has object heights of0.9 and 1.0, respectively, at the upper and lower parts of the screenand this difference is about 8%. The small difference in these twoobject heights serves to have substantially equal ratios of peripherallight quantities on the whole screen, thus to obtain uniform brightnesson the screen without luminance unevenness on the upper and lower partsof the screen.

As apparent from the drawings illustrating the lens characteristics, theprojection lens apparatus according to the present inventionsatisfactorily compensates various kinds of aberration, while thecompactness and the back focus of the projection lens apparatus areachieved. That is, the projection type image display apparatus equippedwith the projection lens apparatus according to the present inventionoffers an image with high resolution, which is uniformly bright even onthe periphery of the screen.

1. A projection type image display apparatus comprising: an imagedisplay element outputting an image ray; a projection lens apparatus forperforming overhead projection of the image ray from said image displayelement, said projection lens apparatus having a plurality of lenselements; a reflection mirror reflecting the image ray from saidprojection lens apparatus; and a screen on which the image ray reflectedby said reflection mirror is projected; wherein an optical axis of saidprojection lens apparatus is decentered from a center of said screen. 2.A projection type image display apparatus according to claim 1, whereinsaid image display element is a micro mirror display element providedwith a plurality of micro mirrors.
 3. A projection type image displayapparatus according to claim 1, wherein said image display element is aliquid crystal display element.
 4. A projection type image displayapparatus according to claim 3, wherein the optical axis of saidprojection lens apparatus is decentered on the center of said screen. 5.A projection type image display apparatus according to claim 1, whereinsaid screen includes a Fresnel screen, and a center of the Fresnelscreen is decentered from the center of said screen.
 6. A projectiontype image display apparatus comprising: an image display elementoutputting an image ray; a projection lens apparatus for performingoverhead projection of the image ray from said image display element,said projection lens apparatus having a plurality of lens elements; areflection mirror reflecting the image ray from said projection lensapparatus; and a screen including a Fresnel screen and on which theimage ray reflected by said reflection mirror is projected; wherein anoptical axis of said projection lens apparatus is decentered upward froma center of said screen, and a center of said Fresnel screen isdecentered from the center of said screen.
 7. A projection type imagedisplay apparatus comprising: an image display element outputting animage ray; a projection lens apparatus for performing overheadprojection of the image ray from said image display element, saidprojection lens apparatus having a plurality of lens elements; areflection mirror reflecting the image ray from said projection lensapparatus; and a screen on which the image ray reflected by saidreflection mirror is projected; wherein the image ray on an optical axisof said projection lens apparatus reflected by said reflection mirror isprojected upward from a center of said screen.
 8. A projection typeimage display apparatus according to claim 7, wherein said image displayelement is a micro mirror display element provided with a plurality ofmicro mirrors.
 9. A projection type image display apparatus according toclaim 7, wherein said image display element is a liquid crystal displayelement.
 10. A projection type image display apparatus according toclaim 7, wherein said screen includes a Fresnel screen, and a center ofthe Fresnel screen is decentered from the center of said screen.